Steam methane reforming to produce a hydrogen and carbon monoxiderich synthesis gas is well known in the prior art. In addition, it is known to use primary reformation for the catalytic conversion of methane and steam to produce hydrogen and carbon monoxide followed by secondary reforming in a thermal, partial oxidation of methane to produce a hydrogen and carbon monoxide-rich synthesis gas.
It is also known to produce alcohols by various processes including the catalytic reaction of methane to produce methanol.
Today the commercial production of higher alcohols (C.sub.3 to C.sub.13) is by the OXO process. In the OXO process, an olefin is reacted with gas in the presence of a cobalt or rhodium catalyst to produce an aldehyde that is one carbon atom longer than the olefin. The aldehyde is then reacted with hydrogen (hydrogenated) over a cobalt or nickel catalyst to produce an alcohol. Thus, in order to produce propanol. the olefin, ethylene, is fed to the process. The general form of the pertinent reactions are: ##STR1##
Drawbacks of this current OXO process are:
(i) It produces only from C.sub.3 to C.sub.13 alcohols. C.sub.1 (methanol) and C.sub.2 (ethanol) cannot be produced by this process, since olefin feeds of one carbon atom shorter length than the alcohols do not exist.
(ii) The process is dependent on olefin feedstock, which is not a stable compound in terms of availability and costs.
(iii) It is a complicated process involving two steps first to manufacture aldehyde from olefin and then hydrogenating the aldehyde to make alcohols.
For commercial production of NH.sub.3, the synthesis gas which enters the ammonia synthesis loop is produced by reforming natural gas and steam in the primary reformer and in the secondary reformer where a proper (stoichiometric) amount of air is introduced. The raw reformer synthesis gas is further processed by two-stage carbon monoxide shift conversion followed by removal of carbon dioxide with MEA, carbonate or other physical adsorbent solution. Residual carbon oxides which are poisons to the ammonia synthesis catalyst are converted to methane via methanation.
The synthesis gas which enters the ammonia synthesis loop is relatively free of CO and CO.sub.2, but contains impurities of methane and argon. These impurities are inerts in the ammonia synthesis process and must be purged to eliminate buildup in the synthesis loop. The purge results in a loss of valuable reactants, in addition to inerts. The buildup of inerts also results in a larger recycle stream requiring greater recompression and a larger sized synthesis reactor and loop.
The following attempts have been made in the past to overcome the drawbacks mentioned above.
(i) Currently, the production of C.sub.3 through C.sub.13 alcohols is divided into 96% by the OXO process, 4% by the Ziegler oligomerization process and only minor amounts by methanolysis of natural oils or fats. Methanol and ethanol are produced separately individually. The current state-of-the-art methanol process is the ICI low-pressure process, licensed by Imperial Chemical Industries PLC. Ethanol is produced by direct hydration of ethylene by the use of demineralized water, a process licensor is HULS AKTIENGELSELLSCHAFT, West Germany.
(ii) In the NH.sub.3 process, the purge gas stream is treated to recover hydrogen which can be recyled back to the ammonia loop. This approach only solves the problem of loss of reactant in the purge. The purge stream can be sent through a membrane unit, cryogenic unit or PSA to recover hydrogen, all of which have been applied commercially in this service.
In contrast to these prior art processes, the process of the present invention provides an optimized technique for carbon monoxide-sourced production of higher alcohols, methanol and the hydrogen-sourced production of ammonia by integrating various unit operations of the synthetic route. The present invention allows the concise control of synthesis gas composition, most typically the hydrogen to carbon monoxide ratio, as required for the different product productions whereby flexibility and optimized plant efficiency is achieved. These advantages will be more clearly delineated below.